The White House has drafted an executive order for President Donald Trump’s signature that would instruct federal antitrust and law enforcement agencies to open probes into the practises of Alphabet Inc’s Google, Facebook Inc, and other social media companies.

The order is in its preliminary stages and has not yet been run past other government agencies, said a White House official.

A draft of the document instructs US antitrust authorities to “thoroughly investigate whether any online platform has acted in violation of the antitrust laws”.

It instructs other government agencies to recommend within a month after it is signed, actions that could potentially “protect competition among online platforms and address online platform bias”.

The document does not name any companies. If signed, the order would represent a significant escalation of Trump’s aversion to Google, Facebook, Twitter and other social media companies, whom he is publicly accused of silencing conservative voices and news sources online.

The press offices of Google, Facebook and Twitter did not respond Saturday to emails and telephone calls requesting comment.

“Social Media is totally discriminating against Republican/Conservative voices,” Trump said on Twitter in August. “Speaking loudly and clearly for the Trump Administration, we will not let that happen. They are closing down the opinions of many people on the RIGHT, while at the same time doing nothing to others.”

Social Media is totally discriminating against Republican/Conservative voices. Speaking loudly and clearly for the Trump Administration, we won’t let that happen. They are closing down the opinions of many people on the RIGHT, while at the same time doing nothing to others.......

Social media companies have acknowledged in congressional hearings that their efforts to enforce prohibitions against online harassment have sometimes led to erroneous punishment of political figures on both the left and the right, and that once discovered, those mistakes have been corrected. They say there’s no systematic effort to silence conservative voices.

The draft order directs that any actions federal agencies take should be “consistent with other laws” – an apparent nod to concerns that it could threaten the traditional independence of US law enforcement or conflict with the First Amendment, which protects political views from government regulation.

“Because of their critical role in American society, it is essential that American citizens are protected from anticompetitive acts by dominant online platforms,” the order says. It adds that consumer harm – a key measure in antitrust investigations – could come “through the exercise of bias.”

A Pew Research Centre survey earlier this year found that 72 per cent of Americans, and 85 per cent of Republicans, think it’s likely that social media companies intentionally censor political viewpoints that those companies find objectionable.

Even on the right, however, there are misgivings about a Trump administration crackdown on the companies.

On Friday, libertarian-leaning groups including FreedomWorks and the American Legislative Exchange Council sent a letter to Sessions expressing “fear” that his “inquiry will be to accomplish through intimidation what the First Amendment bars: interference with editorial judgment.”